An optical method using a colorimeter for an evaluation of discoloration and fading of colors in a weathering (light-fastness) test has been created. However, it has been mainly used for a grade judgement of fastness in various industrial fields, such as in the dyeing industry.
In the visual sense, judgement of a sample color that is approximate to black or to another dark sample color is apt to be difficult, and saturation, lightness and color difference are likely to be judged to be smaller values if an illumination with a normal light source D65, etc., is low. Therefore, the selection of brightness is of importance in the evaluation of colors.
Evaluation of discoloration and fading with existing colorimeters is made by using a colorimetric value after adjustment to a standard value with an accessorial standard plate, irrespective of the brightness/darkness of the sample. The present invention relates to an illumination (luminance) variable calorimetric method and a colorimeter in which the illumination (luminance) of a sample surface is adjusted by taking the brightness/darkness of the sample or the state of hue, saturation and lightness of the sample into consideration when determining the colorimetric value.
The conventional colorimeters (e.g. FIG. 4) are those which measure various measurement values of colors of reflecting and transmitting objects under conditions of standard lights A, C and D65, and so forth. However, these conventional calorimeters do not determine the three attributes (hue, saturation and lightness) of a color, a colorimetric value and a color difference value corresponding to a change of illumination when the illumination of a sample surface is changed to determine an optimum illumination range in consideration of the attributes of the sample surface. None of the conventional colorimeters have solved these problems to the best knowledge of the present inventor.
The judgement of colors and the evaluation of discoloration/fading, contamination, etc., have been made by the visual sense judgement of people, while optical methods using a colorimeter have also been carried out. The conventional calorimeters involve a problem in that they cannot determine the three attributes (hue, saturation and lightness) of a color, the calorimetric value, and the color difference value corresponding to the change of illumination when the illumination is changed so as to determine an optimum illumination range in consideration of the attributes of the sample surface. In the case of the visual sense judgement of discoloration, fading, etc., the grading of the fading and the judgement of the color difference pairs are difficult, particularly when the color of a sample is approximate to black or is a dark color, or when the illumination of the light source used for illumination is low.
The inventor of the present invention has developed a system which can change the illumination (luminance) of a normal light source inside a calorimetric standard illuminant, apparatus. As a result, the judgement results of a plurality of observers become close to being identical by increasing the illumination of the normal light source when the sample has a dark color.
The present inventor has developed the technical concept described above and has further developed a calorimeter having the function of varying the illumination so as to bring both the evaluation results of a color into conformity in the evaluation of color judgement, etc.
The illumination variable calorimetric method and the calorimeter described above are equipped with a light power adjustment mechanism and an illumination measurement light receiver, and eliminate the drawbacks of conventional colorimeters and the disadvantages resulting from a color discrepancy between the visual sense and the calorimeter.
The present invention relates to the measurement of colors which compares the mode of appearance of a color image by the visual sense and the mode of appearance of the color from a colorimetric value by a colorimeter with each other, makes it possible to establish a correspondence relationship between each of the evaluation results, and reflects the difference of the modes of appearance of the color for the observer on the calorimeter depending on high and low illumination.
The colorimeter comprises an optical portion shown in FIG. 1 and a measurement portion shown in FIG. 3. The optical portion comprises a measurement optical path 7 and a compensation optical path 6. In addition, an illumination adjustment mechanism 12 for varying the illumination, and an illumination measurement light receiver 10 are both provided in the measurement optical path 7.
After the illumination is adjusted to a predetermined value such as 6,310 1xc3x97 while a standard plate having high weatherability is placed on the surface of a sample table 8 of the optical portion, adjustment of a standard value put on the standard plate is effected. A sample 14 is placed on the sample table 8 and a calorimetric value at 6,310 1xc3x97 is measured. The illumination of the sample surface is varied to 3,160, 2,040, 1,000 and 540 1xc3x97, for example, by the illumination adjustment mechanism 12 and the illumination measurement light receiver 10.
The illumination variable calorimetric method and the colorimeter of the present invention measure changes in the three attributes (hue, saturation and lightness) of the surface color of the same sample, each calorimetric value and the color difference value for each color difference pair with respect to the change of illumination described above, and displays them.